Mapping the Globe's Soils

Long left in the dust by their peers in climate research, a small group of soil scientists is spearheading an effort to apply rigorous computer analysis to the ground beneath our feet.

Their goal: to produce a digital soil map of the entire world.

It is a daunting task. In many parts of the world, such as Africa and South Asia, knowledge of soil is sketchy at best, relying on fading paper maps. And without accurate soil information, it is difficult for planners to know where crops are best grown, or for climate modelers to predict how much carbon might be released from soil into the atmosphere.

"The scientific disciplines are crying for this information," said Alfred Hartemink, the project's coordinator and a soil scientist at ISRIC, a globally focused soil institute funded by the Dutch government.

Climate scientists, hydrologists, agronomists and ecologists all want to feed these data into their models, Hartemink said, so they can better address big questions: What happens if there's drought in the Midwest? Or if huge swaths of land are given up for biofuels?

"People are realizing that food comes from the land," Hartemink said. "And if you want to end hunger, then you need to know your soil and the soil needs to be in a good condition."

The project, known as GlobalSoilMap.net, has received roughly a million dollars in seed money from the Bill and Melinda Gates Foundation. As Hartemink put it, "It's a map, and [Bill] likes maps. It's digital, and he likes digital." An offshoot of the effort, the Africa Soil Information Service, has also received $18 million from the foundation.

Soil information is particularly poor in Africa. Indeed, scientists know more about the soils of Mars than Africa, said Pedro Sanchez, a soil scientist and author of a paper published today in Science that describes the team's work.

"We have the rovers in Mars, and they transmit the spectral signature of soil and rocks," Sanchez said. For instance, "we know the soils of Mars have a lot of salinity." And yet this modern technology has not been applied to large-scale soil surveys in Africa, he added.

The project would largely base its digital map on high-tech extrapolations from existing, pre-digital maps. If successful and funded -- scientists estimate the map would cost more than $200 million -- the map could provide snapshots of the land over time, in response to changing conditions.

"We spend a fair amount of time wondering whether the data we are using is correct," Lawrence said. Often, when models go awry, this is due to incorrect soil data, he added.

Many countries, including the United States, do have accurate legacy maps of their soils, many of which have been scanned into computers. But at low resolutions, these maps have a fatal flaw, scientists say. The land is split into polygons -- most maps look like multicolored states after extreme bouts of gerrymandering -- and within these polygons, the soil is assumed to be uniform. There is no probability.

As any researcher will tell you, scientists need probability. And so, building from these polygon maps, the project will marshal the statistical force of modern computing and combine it with satellite data obtained over the past decades that reveal plant cover, surface temperature and elevation, as well as existing climate data.

In the end, what will be produced is a high-resolution soil map rendering data in pixels, tiny digital squares. Rather than indulge in the arcana of soil terminology ("Honeoye silt loam," "mesic Glossic Hapludalf"), each sample will list in probable terms the properties of the soil: its water storage, carbon density, acidity and density, and even its electrical conductivity.

The map would have a resolution of two football fields, 100 meters square, said Bob MacMillan, who is taking over scientific coordination of the project next month.

Several pilot projects are under way to support their theories, including on the border between North Dakota and Manitoba, Canada, and in the Danube region. Australia is the most advanced soil mapper, MacMillan noted, effectively testing their model on the entire continent.

It did not go entirely smoothly.

According to the project's managers, "There were areas where they got it pretty good, and areas where they got it pretty badly," MacMillan said. The team is refining its models now, and the project's initial results are online, providing a rough model of maps to come.

African soil

The largest test bed for the digital map is the African project, announced in January. Sanchez, a noted soil scientist, also leads the Millenium Villages project at the Earth Institute of Columbia University, a community development program that works with African villages to build sustainable farms. Having a robust digital map would be a boon for planners, he said.

Currently, much of Africa suffers from a shortage of phosphorus in its soil, an essential nutrient used by plants for photosynthesis and energy transport. Typically, phosphorus, depleted by harvests and erosion, is replenished by fertilizer; in Africa, however, fertilizer use sits at 10 percent of the world average.

Put another way: Thanks to its poor soil, the average farm in Africa produces 1 ton of corn. In the United States and Europe, the average is 8 tons, according to Sanchez.

To build the African map, the service will compile all existing data sets and then sample 60 sites across sub-Saharan Africa and Madagascar -- a region covering 18.1 million square kilometers. Their "spatially stratified random sampling approach," the service says, will provide the first "unbiased sample of the subcontinent."

In a continent that is home to nearly a billion people and diverse ecosystems, 60 sites may seem like a small sample. This is where the technology comes in, the service's supporters say. Eventual testing will prove their accuracy, but, as MacMillan notes, analog soil maps are already unreliable, with rates hovering between 55 and 65 percent.

"What we're doing here is not so much magic, it is replicating and validating our logic," MacMillan said.

This month, the project is establishing a North African base in Jordan, and around the world -- academic centers in the United States, Brazil, China, Australia, Kenya and France are collaborators -- its researchers are "chasing money," Hartemink said.

The map has the growing support of scientists in the United States, said Karl Glasener, the director of science policy for the Soil Science Society of America.

At the Group of Eight industrial nations meeting last month, President Obama said he would ask Congress to double U.S. agricultural development assistance to more than $1 billion in 2010.

"With the president's announcement of new support for agricultural development assistance," Glasener said, "perhaps the opportunity will arise to channel funding to the global digital mapping project."